(a) Field of the Invention
The present invention relates to a system and method for processing crank angle signals.
(b) Description of the Related Art
Increasingly precise electronic control of engines is being employed in recent times to enhance overall engine performance, decrease fuel consumption, limit exhaust emmisions and improve ride comfort. Examples of such control include fuel injection control, ignition timing control and engine misfire control.
To perform such precise engine control, a system and method for processing crank angle signals is required to precisely detect engine rpm changes, rotation angle of a crankshaft, and a cylinder in which a misfire occurs. In the conventional system and method for processing crank angle signals, a plurality of evenly-spaced teeth are provided on a sensor wheel, which is connected to a crankshaft to rotate with the same. A predetermined space at a particular location is provided where the teeth are formed on the sensor wheel (i.e., where teeth are missing), and the space is positioned so that it may be used as a control reference location, indicating top dead center (TDC) for a particular piston within its cylinder. It is from this point that a predetermined crank angle is measured and converted into a number of rotations of the crankshaft.
Also, a phase sensor determines which piston is at TDC of a compression stroke when the crank angle sensor generates a signal, and the cylinder identity signal is generated on every rotation of a camshaft. On the basis of this information, an engine control system performs fuel injection control, ignition timing control, and engine misfire control.
FIG. 1a shows a crank angle signal sensing method in the conventional system.
In the crank angle signal sensing method shown in FIG. 1a, a distance between a tooth and a bottom of a space between an adjacent tooth of the sensor wheel connected to the crankshaft is detected by a magnetic pickup, with a high value corresponding to the teeth and a low value corresponding to the bottom of the space between the teeth. Accordingly, in the case where one revolution of the engine corresponds to 16 teeth and a space of two missing teeth, tooth periods generated every 20xc2x0 are observed, and if a tooth period is greater than or equal to twice a previous period, a missing tooth period is deemed to have occurred.
If it is determined that a missing tooth period has occurred, it is determined that a particular piston is at a TDC. The moment this occurs is used as a standard location, and from this point, a time for a 180xc2x0 crankshaft rotation is measured, and this information is used to determine a number of rotations per minute (rpm).
FIG. 1b shows a waveform of a cylinder identity signal used to discern which cylinder is at a compression TDC.
The phase sensor is linked with the camshaft to generate a cylinder identity signal with every rotation of the camshaft. When a low value of the cylinder identity signal is set to signify the compression stroke of a first cylinder, in the case where the missing tooth period of the crank angle sensor is detected while the cylinder identity signal is low, it is deemed that the first cylinder has reached TDC on its compression stroke.
However, since engine speeds can abruptly experience a certain degree of variation in a low speed state or low temperature state where viscosity resistance of the oil increases, there occurs a significant increase in how such variation in engine speed influences the determination of the missing tooth period. That is, with such circumstances in the prior art method, a ratio of the missing tooth period to a previous tooth period becomes less than two such that the reliability of determining the missing tooth period is reduced.
Further, with vehicles using engines of a small displacement, since the number of teeth provided on the sensor wheel is reduced as a result of size limits, cold starts are not possible.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a system and method for processing crank angle signals in which the reliability of determining a missing tooth period is improved in both low speed and low temperature states, and in which cold starts are possible.
To achieve the above object, the present invention provides a system and method for processing crank angle signals. The system comprises a crank angle sensor for converting a rotation of a crankshaft into analog signals; a switching circuit for converting the analog signals into crank angle signals; a timer/counter for detecting a number of pulses and tooth periods of the crank angle signals; a phase sensor for converting a rotation of a camshaft into cylinder identity signals and outputting the cylinder identity signals; and an electronic control unit for receiving the crank angle signals and the cylinder identity signals and using the signals to determine cylinder identity and rpm.
According to a feature of the present invention, the crank angle sensor comprises a sensor wheel having a plurality of teeth formed at predetermined intervals around a circumference of the sensor wheel, the sensor wheel being connected to the crankshaft; and a magnetic pickup for detecting variations in a magnetic field caused by a difference in distance between the teeth of sensor wheel and the magnetic pickup, and between a bottom portion between the teeth of the sensor wheel and the magnetic pickup, the difference in distance occurring as a result of a rotation of the sensor wheel.
According to another feature of the present invention, the timer/counter establishes points at which the cylinder identity signals, which are output from the phase sensor, undergo inversion from high to low states or vice versa as reference positions, then starting from the reference positions counts and outputs the pulses of the crank angle signals, and calculates and outputs a time until a predetermined number of the pulses is counted.
According to yet another feature of the present invention, the electronic control unit receives the number of pulses of the crank angle signals output from the timer/counter, then identifies a cylinder corresponding to the input pulses and calculates engine rpm based on the time until the predetermined number of the pulses is counted as determined by the timer/counter.
The method comprises the steps of inputting a crank angle signal and a cylinder identity signal; determining if the cylinder identity signal has undergone inversion from a high to low state or vice versa; establishing a point at which the cylinder identity signal undergoes inversion as a reference position; counting a predetermined number of pulses of the crank angle signal after the reference position if the cylinder identity signal does not undergo inversion; and identifying a point at which the predetermined number of pulses of the crank angle signal is counted as a point corresponding to a particular cylinder.
According to a feature of the present invention, the cylinder identity signal is a signal having a single short pulse, a signal having a pulse extending over half a period of the cycle, or a signal having two pulses of different widths.
In another aspect, the method comprises the steps of inputting a cylinder identity signal output from a phase sensor and a crank angle signal to a timer/counter, the cylinder identity signal being a signal having a single short pulse; determining, by the timer/counter, if the pulse of the cylinder identity signal has undergone inversion from low to high; establishing, if it is determined that the pulse of the cylinder identity signal has undergone inversion, a point at which the cylinder identity signal undergoes inversion as a reference position and calculating rpm at this point, the establishment of the reference position and calculation of rpm being performed in an electronic control unit; counting, one at a time, a number of pulses of the crank angle signal by the timer/counter if the cylinder identity signal does not undergo inversion; determining if the number of pulses of the crank angle signal has reached a predetermined number; determining that a particular cylinder has reached TDC at a point where the number of pulses of the crank angle signal reaches the predetermined number; and initializing the timer/counter when the number of pulses of the crank angle signal counted by the timer/counter and a result of dividing the number of pulses of the crank angle signal during one period by a number of cylinders are the same.
According to a feature of the present invention, the method further comprises the step of continuously counting the pulses of the crank angle signals during one period without initializing the timer/counter.
In yet another aspect, the method comprises the steps of inputting a cylinder identity signal output from a phase sensor and a crank angle signal to a timer/counter, the cylinder identity signal being a signal having a pulse extending over half a period of the cycle; determining, by the timer/counter, if the pulse of the cylinder identity signal has undergone inversion; initializing the timer/counter, then establishing, by an electronic control unit, a point at which the cylinder identity signal undergoes inversion as a reference position, the initialization of the timer/counter and the establishing of the reference position being performed if it is determined that the pulse of the cylinder identity signal has undergone inversion from low to high; counting a number of pulses of the crank angle signal by the timer/counter if the cylinder identity signal does not undergo inversion; determining if the number of pulses of the crank angle signal has reached a predetermined number for engine control; determining that a particular cylinder has reached TDC at a point where the number of pulses of the crank angle signal reaches the predetermined number; determining if the number of pulses of the crank angle signal counted by the timer/counter equals a sum of the predetermined number of pulses of the crank angle signal and a result of dividing the number of pulses of the crank angle signal during one period by a number of cylinders; and determining that a subsequent cylinder has reached TDC by the electronic control unit at a point where the number of pulses of the crank angle signal counted by the timer/counter equals the sum.
According to a feature of the present invention, in the step of determining, by the timer/counter, if the pulse of the cylinder identity signal has undergone inversion, a point where the pulse of the cylinder identity signal undergoes inversion from high to low and from low to high is established as the reference position.
In still yet another aspect, the method comprises the steps of inputting a cylinder identity signal output from a phase sensor and a crank angle signal to a timer/counter, the cylinder identity signal being a signal having two pulses of different widths; determining, by the timer/counter, if the pulse of the cylinder identity signal has undergone inversion from low to high; initializing the timer/counter, establishing a point at which the cylinder identity signal undergoes inversion as a reference position, and counting a number of high values of the crank angle signal during which the cylinder identity signal is in a high state, with the initializing, establishing, and counting occurring if it is determined that the pulse of the cylinder identity signal has undergone inversion from low to high, and the reference position and the number of high values of the crank angle signal being output to an electronic control unit; counting a number of pulses of the crank angle signal for controlling the engine by the timer/counter if the cylinder identity signal does not undergo inversion from low to high; determining if the number of pulses of the crank angle signal has reached a predetermined number to control the engine; determining that a particular cylinder has reached TDC at a point where the number of pulses of the crank angle signal reaches the predetermined number; performing cylinder identification based on (a) the reference position stored in the electronic control unit, (b) the number of pulses of the crank angle signal counted when the cylinder identity signal is in a high state, and (c) the number of pulses of the crank angle signal for controlling the engine; determining if the number of pulses of the crank angle signal counted when the cylinder identity signal is in a high state equals a sum of the number of pulses of the crank angle signal for controlling the engine and a result of dividing the number of pulses of the crank angle signal during one period by a number of cylinders; and determining by the electronic control unit that a cylinder subsequent to that identified in the step of performing cylinder identification has reached TDC at a point where the number of pulses of the crank angle signal counted when the cylinder identity signal is in a high state.
According to a feature of the present invention, in the step of performing cylinder identification, if there is a number of counted pulses of the crank angle signal during a long high portion of the cylinder identity signal, a point at which the number of pulses of the crank angle signal reaches a predetermined number is determined to be where a particular cylinder reaches TDC.